1. Field of the Invention
This invention relates generally to catheters for performing vascular intervention surgery. More specifically, the present invention relates to catheters used in coronary atherectomy surgery.
2. Description of the Related Art
Medical science has long sought effective treatments for disease conditions involving stenosis (narrowing or obstruction) of the lumen (interior passage of the artery) of an artery. This condition, known generally as an occlusion, is found in patients suffering from atherosclerosis (accumulation of fibrous, fatty or calcified tissue in the arteries). An occlusion can manifest itself in hypertension (high blood pressure), ischemia (deficiency of circulation), angina (chest pain), myocardial infarction (heart attack), stroke or death. An occlusion may be partial or total, may be soft and pliable or hard and calcified, and may be found at a great variety of sites in the arterial system including the aorta, the coronary and carotid arteries, and peripheral arteries.
Of particular interest to cardiac medicine are the often disabling or fatal occlusions occurring in the coronary arteries (arteries supplying the heart). Traditionally, coronary artery occlusions have been treated by performing coronary bypass surgery, in which a segment of the patient""s saphenous vein is taken from the patient""s leg and is grafted onto the affected artery at points proximal (upstream) and distal (downstream) to the occluded segment. The bypass often provides dramatic relief. However, it entails dangerous open chest surgery and a long, painful, costly convalescence in the hospital. Moreover, with the passage of time, the patient""s bypass saphenous vein graft can also become occluded. If the patient has another saphenous vein, a second bypass procedure may be performed, once again entailing open chest surgery and prolonged hospitalization. Thereafter, if the underlying atherosclerotic disease process is not controlled, the prognosis is dismal.
Newer, minimally invasive procedures are now preferred in the treatment of arterial occlusions. These procedures use a catheter, a long, thin, highly flexible device which is introduced into a major artery through a small arterial puncture made in the groin, upper arm, or neck and is advanced and steered into the site of the stenosis. At the distal end of the catheter, a great variety of miniature devices has been developed for operating upon the stenosed artery.
The more popular minimally invasive procedures include percutaneous transluminal coronary angioplasty (PTCA), directional coronary atherectomy (DCA), and stenting. PTCA employs a balloon to mechanically dilate the stenosis. In PTCA, a steerable guidewire is introduced and advanced under fluoroscopic observation into the stenosed artery and past the stenosis. Next, a balloon-tipped catheter is advanced over the guidewire until it is positioned across the stenosed segment. The balloon is then inflated, separating or fracturing the atheroma (stenosed tissue). The hoped-for outcome is that, over time, the lumen will stay open.
In directional coronary atherectomy, a catheter containing a cutter housed in its distal end is advanced over the guidewire into the stenosed segment. The housing is urged against the atheroma by the inflation of a balloon, so that part of the atheroma intrudes through a window in the side of the housing. Under fluoroscopic observation, the cutter is used to shave away the atheroma. The shavings are collected in the nose cone of the housing and withdrawn along with the catheter or flushed out of a flushing lumen running the length of the device.
All of these devices, however, suffer from one or more of the following disadvantages. The first of these disadvantages is large size. The large shaft profiles of these existing atherectomy catheters makes it necessary to use catheters of large size. This large size makes it difficult, if not impossible, to use these catheters in the smaller and more tortuous coronary vessels. The second of these disadvantages is torquability of the known catheters. Indeed, the poor responsiveness of the distal end of known catheters to rotational inputs applied at the proximal end (this poor response being referred to herein as a high torque ratio, a superior response being referred to herein as low torque ratio) is the result of the elliptical cross-sectional shape of their catheter shafts. This renders the manipulation, correct placement and orientation of the distal end of the catheter device within the patient""s vessels difficult. Known atherectomy catheters are also limited in the amount of atheroma tissue they can retrieve. This is due, in part, to the low cut tissue storage capacity of known nose cones.
Balloon-based catheter stabilization systems also have a number of drawbacks. The most important of these is that, in some applications, the balloon tends to slip into the area of the vessel from which a portion of atheroma was just cut. This is because, when atheroma is cut, it creates a low area, or depression relative to the remainder of the occlusion. The balloon, by virtue of its shape and texture, naturally tends to slip into that area. This can render the proper positioning of the housing window or opening difficult. Moreover, conventional balloon-based catheters can only be inflated to a predetermined diameter. This limits their application to a specific vessel lumen diameter.
There have been a number of mechanical stabilization systems proposed, notably based upon complicated structures or shape memory metals which alter their shape when a current is applied to them. These are disclosed in Conley et al., U.S. Pat. No. 5,527,325 and Klein et al., U.S. Pat. No. 5,279,565, the specifications of which are incorporated by reference. However, these suffer from undue complexity and high cost of manufacture.
It is, therefore, an object of the present invention to provide an over-the-wire catheter device of small size and substantially circular cross section.
It is another object of the present invention to provide a catheter with improved maneuverability.
It is an additional object of the present invention to provide a catheter having improved torquability.
It is an additional object of the present invention to provide an alternative to balloon-based catheter stabilization systems.
In accordance with the above objects and those that will be mentioned and will become apparent below, the over-the-wire catheter device for use in a biological conduit according to the present invention comprises:
a substantially round housing torque cable having a proximal end and a distal end;
a housing connected to the distal end of the housing torque cable, the housing including a window for invaginating biological tissue;
a cutter torque cable, the cutter torque cable being concentric with the housing torque cable;
a cutter movably attached to a distal end of the cutter torque cable to operate within the housing, the window exposing the cutter;
a guidewire concentrically disposed within the cutter torque cable and the cutter;
a balloon disposed opposite the window; and
a balloon inflation lumen disposed inside the housing torque cable and emerging outside the housing torque cable adjacent the proximal end of the housing to provide fluid communication with the balloon.
An advantage of this embodiment is that the positioning of the catheter within the biological vessel is facilitated by disposing the balloon inflation lumen and the cutter torque cable within the housing torque cable.
According to an exemplary embodiment, the nose cone comprises at least one longitudinal or wire-reinforced rib for strengthening the nose cone. An advantage of this embodiment is that the at least one longitudinal rib increases the nose cone""s column strength and torsional strength. The nose cone may be made of nylon or polyurethane. According to another exemplary embodiment, the nose cone may have a cylindrical shape over at least 70% of its length, the nose cone thereafter tapering toward its distal end. An advantage of this exemplary embodiment is that the cylindrical shape allows a large volume of atheroma to be stored in the nose cone. To facilitate positioning the catheter within the biological conduit, the nose cone is marked with barium or with other radio-opaque material. In an exemplary embodiment of the present invention, the housing is made from at least one material selected from the group consisting of steel, ceramic, THERMAT, titanium and zirconium.
In another exemplary embodiment, the catheter device for use in a biological conduit according to the present invention comprises:
A substantially round housing torque cable having a proximal end and a distal end;
a housing connected to the distal end of the housing torque cable, the housing including a window for invaginating biological tissue;
a cutter torque cable concentrically disposed within the housing torque cable;
a cutter movably attached to a distal end of the cutter torque cable to operate within the housing, the window exposing the cutter;
a nose cone for collecting and storing atheroma cut by the cutter;
a resilient stabilizing member disposed outside and opposite the housing window, the stabilizing member having a proximal end and a distal end, the distal end of the stabilizing member being attached to a distal end of the housing, and
a stabilizing cable for selectively bowing and flattening the stabilizing member, the stabilizing cable being disposed within a cable lumen running within the housing torque cable and emerging adjacent a proximal end of the housing to allow the stabilizing cable to connect to the proximal end of the stabilizing member. When the stabilizing cable is advanced in a distal direction, the stabilizing member bows away from the housing to stabilize the catheter housing within the biological conduit, and when the stabilizing cable is retracted in the proximal direction, the stabilizing member flattens about the housing to allow free movement of the catheter housing within the biological conduit. This stabilizes the catheter according to the present invention without the use of an inflatable balloon.
The present invention is also a system for stabilizing a catheter within a biological conduit, the catheter having a proximal end and a distal end, the catheter further having a housing disposed at the distal end of the device, the housing including a window exposing a work element. The system comprises:
a resilient stabilizing member disposed outside and across the housing of the catheter, the stabilizing member having a proximal end and a distal end, the distal end of the stabilizing member being attached to a distal end of the housing, and
a stabilizing cable for selectively bowing and flattening the stabilizing member, the stabilizing cable being disposed within a cable lumen within the catheter, the cable lumen emerging adjacent a proximal end of the housing to allow the stabilizing cable to connect to the proximal end of the stabilizing member. When the stabilizing cable is advanced in a distal direction, the stabilizing member bows away from the housing and against the biological conduit to stabilize the housing, and when the stabilizing cable is retracted in a proximal direction, the stabilizing member flattens about the housing to allow free movement of the device within the biological conduit.
According to an exemplary embodiment, the resilient stabilizing member is a thin strip of relatively hard, resilient material. This material may be, for example, stainless steel, polycarbonate or polyimide. According to an exemplary embodiment, the resilient stabilizing member is disposed outside the housing about 180 degrees away from the housing window.